The invention relates to improvements in methods and apparatus for separation of a magnetic material from a suspension, and more particularly to utilizing a matrix through which is passed a fluid stream of magnetizable and non-magnetizable particles with the matrix contained in a canister positioned in a magnetic field. When a matrix has been loaded with magnetic material, the canister is removed and a new canister with a matrix is positioned in the magnetic field while the previously loaded canister is cleared of magnetic material.
In accordance with the practice of the invention, a strong field separation is employed wherein a canister contained matrix is utilized with the matrix being a low-retentivity material. The matrix within the canister is placed within a magnetic coil which is flooded by a fluid suspended particle solution and strong magnetic field gradients rise at the surface of the structure material as a consequence of the magnetization thereof. These magnetic field gradients together with the superimposed field exercise strong attractive forces on the magnetizable particles and retain such particles at the matrix surface. When the matrix is loaded, it must be cleaned. In accordance with prior practices, the magnetic field is shut off or the matrix removed outside of the environment of the magnetic field for cleaning. To contain the fluid the matrix is located in a container which preferably is of a size to fit within a coil generating the magnetic field and the container is provided with connections for the intake and discharge of the fluid suspension.
Matrix magnetic separators are utilized in what is known as a reciprocating canister method (RC method). This is a cyclical method. The adhering particles must be removed from the matrix at regular intervals from the canisters traversed by the fluid suspension. It has been proposed that the field not be disconnected but that the canister be withdrawn from the field, utilizing a full field, and that the canister and matrix be washed outside of the field. See, M. Parker, "Recent Developments in High Field Magnetic Separation", page 3, in Electrical and Magnetic Separation and Filtration Technology, Antwerp, May 1984.
Devices which have attempted to perform a magnetic separation in the manner above discussed, and apparatus suitable for this purpose contains a hydraulic actuated canister which also contains dummy canisters which are necessary for the compensation of the forces when the matrix is withdrawn from the magnetic coil. Although the withdrawal of the loaded matrix and replacing it with an unloaded matrix that is arranged in series, the canister pull shortens the dead or nonoperational time which is the time in which no magnetic separation can occur because the canister is displaced and the particle suspension has been switched to a wash agent location. Considerable exertions are needed in order to bring the matrix into an unmagnetized condition. For example, a magnetic shielding in a de-magnetization coil are employed since magnetic coils of the type normally employed exhibit considerable leakage fields in the outside space along their axis. Further devices which effect the intake and discharge of the fluid suspension and of the wash agent into the canister must be arranged to operate on select canisters and to by-pass other canisters arranged in a series. They must take into consideration the magnetic coil and this reduces the available room for the magnetic separation.
In accordance with methods previously employed, the suspension flows through the full cross-section of the matrix only in a direction parallel to the coil axis. This requires an involved design of the coil or in turn of the magnetic yoke in order to maintain a uniform field strength over the cross-section of the suspension.
It is accordingly an object of the present invention to provide a method and apparatus wherein the magnetic separation process has a very short inoperative or dead time and wherein an apparatus is employed which is durable and rugged and capable of continued operation without repair or attention, and wherein the mechanism insures the optimum attraction of a variety of magnetic particles with simple magnetic coils.
A further object of the invention is to provide an improved method and apparatus for magnetic separation in a matrix containing canister wherein the matrix can be cleaned and the continuous cleaning of the matrix to provide a fresh canister to move into the magnetic field is done in a manner so that it does not shorten the inoperative time when a canister is effectively within the magnetic field.
In accordance with the principles of the invention, a plurality of canisters are supported or mounted such that the canisters are positioned parallel to the axis of the magnetic field and the axis of introduction into the operative position before introduction into the magnetic coil. The introduction and discharge of the fluid into and out of the canister proceeds from one axial end. For changing the canister, the canister is moved axially from within the coil and is thereafter pivotally or rotationally moved to a cleaning position and the same rotation or pivotal movement moves an unloaded fresh canister into the coil axis for separation. The unloaded canister is introduced into the magnetic coil in an axial motion from the same direction relative to the coil but in the opposite direction of axial movement relative to the direction in which the previous loaded canister was withdrawn. The mechanism is arranged such that the inlet and outlet of the fluid suspension of magnetic material is at the same end of the canister. The canisters are mounted on a turret arrangement so that they move between positions wherein in one position they are traversed by the fluid suspension of magnetic material and in the other position by a cleaning fluid. In other words, the canisters are moved in the same axial direction, but at a different location, into their effective separation position or their effective cleaning position.
In accordance with the principles of the invention, substantial advantages are achieved over prior art arrangements in that essentially only four movements of the canister are necessary. The movements are axial withdrawal of the canister from the magnetic field, lateral pivotal rotary movement of the loaded canister (relative to the axis of the magnetic field), simultaneous pivotal movement of an empty canister into the axis of the magnetic field and an axial introduction of the canister into the magnetic field from the same side as the withdrawal of the canister. A feature of the arrangement is that it is thereby not necessary to shut off the magnetic field and this is particularly desirable for the use of a superconductive magnet. In the movement of the canisters from the magnetic field to the cleaning location, a turret type of arrangement is preferred wherein the axis of the rotary turret is parallel to the principal axis of the magnetic field. In the arrangement utilized, no valves are required which must be additionally actuated. By contrast, the introduction and exhaust of the suspension into and out of the canister can be controlled in a simplified way with a distributor head which automatically connects to the various canisters in their positions with rotary movement of the turret.
In accordance with the invention, a rotary valve head is employed which allows the canisters to be raised and lowered axially and this is equivalent to or superior to a design wherein the magnets must be raised and lowered and the canisters only are moved in a lateral or rotatable movement or wherein the canisters are stationary and the magnetic coils are moved in their axial direction and perpendicular thereto.
To meet the requirements of certain operations, the loaded canisters are removed as a whole and disposed of. This occurs, for example, when mild radioactive substances are separated. In the majority of applications, however, a loaded canister is cleaned or washed for regeneration. In the simplest case, two canisters are provided for such an operating mode, one being loaded while the other is being cleaned. When the cleanin lasts longer than the loading, a plurality of washing stations are provided for each filling station. With a rotary turret and a stationary valve head, the washing as well as the supplying of magnetic fluid to the canisters can be sequenced automatically with rotation of the turret. Thus, as will be seen by the drawings, two filling positions and at least two cleaning positions can easily be accommodated with a rotary turret.
In addition to the foregoing simplified slurry management and washing, the withdrawal and introduction of the canisters into the magnetic field in a manner which always proceeds from the same axial side also results in that the suspension can be arranged to traverse the magnetic field at least twice. This accomplishes uniform collection of the magnetic material with a magnetic field strength that can vary when coils that are simplified in construction are utilized. In accordance with the principles of the invention, this feature is additionally exploited by providing a canister with chambers. Such chambers are arranged for the sequential flow of fluid and in the sequential chambers, different matrices can be employed. Matrices of different structure and different spatial location with respect to the magnetic field can be utilized arranged so that they are optimum for the separation of specific particles. Thus, if a field strength is employed which is not entirely uniform which is obtainable with simple short coils, such structure does not represent a disadvantage but can instead be used for improving the separating results. It is also possible to lengthen the path that the slurry travels in the canister and this accomplishes a longer exposure to the magnetic field without providing long magnetic coils.
The arrangement of the method and structure is rugged and accommodates servicing. The wash positions are outside of the magnet, and are therefore available for dismantling and changing the matrices. The solenoid magnets and the mechanical structures required which employ a raisable and a rotatable rotary plate with a distributor head can be constructed relatively simple and inexpensive.
Although the spatial arrangements within the concepts of the invention can be varied, an arrangement wherein the coil axis is vertically arranged and the canisters are introduced from below has the advantage that the weight of the canisters and of the support means compensates for the magnetic force with which the canisters are held within the magnetic field of the coil. Moreover, the fact that the magnetic coils are charged by introducing the canisters from only one side enables a compensation of the magnetic force by springs or by dummy loads that are introduced and withdrawn from the other side but which have no fixed connection to the canisters.
During the washing process, the canisters are no longer positioned in the axial extension of the coil but are laterally next to it. Since the lateral scatter field is rather low, measures which heretofore were required for shielding can be eliminated or easy to accomplish.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiment in the specification, claims and drawings, in which: